Sound shield for telephone transmitters



P. s. V ENEKLASEN 2,456,346

SOUND SHIELD FOR TELEPHONE TRANSMITTERS Dec. 14, 1948.

Filed Jan. 24, 1945 Patented Dec. 14, 1948 SOUND SHIELDFOR TELEPHONE TRAN SMITTEBS Paul s veneklasen, Saugus; Mass., assignor-uto the United. States of America as represented by the. Officebf. Scientific Research and. Develop.-

ment

: Application January 24, 194.5,2smar1so-l57a3s7 2 Claims.

-This-inventionrelates to telephones and more particularly to ahand telephone set.

An; object of the invention is to'improve hand telephone sets and to devise a receiver portion of a hand telephone set which is particularly adapted f oruse with. army helmets. Another objectis to incorporate in the transmitter portion of a.handtelephoneset-means for obtaining improved speech communication and noise exclusion. Another. obj ectisto provide asimple, durable-.and'efiicient hand telephone set. Other objects will appear from the followingdescription oftthe drawings and discussion relating thereto.

In the accompanying drawings:

"Fig. lwisa view in-. sideelevation and partial longitudinal-section illustrating the hand telephone set of the invention;

"Fig. 2 isa cross section taken ontheline 2-2 ofFig'; 1; and

.Eig. 3 is a detail front elevational view of a microphonexandnoise shield assembly.

izReferring. morewindetail to the drawings, numeral'iidenotes a framemember for a telephone hand set. .Thelframeiszof tubular construction and; atits middle portion: is providedwithaconventional. switch arrangement which is not disclosed.in detailzin thedrawings. ITheswitch is operated by means of. a switch button 4, partly recessed; in .theframe. member at the inner side thereof.

1 At the lower or transmitter end of the frame member 2 islocated a microphone 5 of the mask type. The microphone is held in place by; means of acap I which is threaded tothe extremity of the frame 2, as is more clearly illustrated at the lower right-handside of Fig. 1. Atthe upper end 9 the frame member isprovidedan'iearphone 6 which may also-be of-conventional design. The earphone is held in place by a receiver cap 8 threaded around the extremity of the frame member.

The receiver cap 8 has snugly fitted around it an ear cushion member ID, preferably formed of a resilient rubber-like material such as for example neoprene or other substances. The cushion. member is characterized by an annular rim H which occurs. inspaced relation tothe base of the cushion, thereby leaving a cavity 14 which permits the annular rimto be depressed. There is thus provided substantial: compliance or yieldability.

;Noise excluding. means have been provided :for at themicrophoneend of the handset. C An indicated in the drawings, numeral 24 indicates a noise shield member formed of soft rubber or :12 rubber-.likermaterialsuchas neoprene or other substances. Thenoise shield-Isaenerally cuplikemember having forwardly-flared flexible sides forming aforwardvoice chamber. Therearward part of thenoiseshield is circular, so: asto engage aroundshouldered; portions 26 of the'microphoneretainer cap- Lwhichcserves asa support for the shield,..asclearly indicated in Figs. land 2.

The volumemf the cavity existingin the noise shield, when, engaged against the face, is, so chosen that'whenrthedevice is used with currently. available microphones, asubstantially .flat frequency response curveis achieved. The reason is that this size of cavity is adapted to: accentuate low frequencies to a. degree suchthat thev microphonehas a reduced or falling response curve.

. The noise shield. member is especially fitted to conform to theshape of the face andthe contour of atransverse section of the noise shield member is oval-shaped for this reason. Inaddition, the forward extremityv of the shield member-is further provided-with upper and lower rolled edges 2'! and 28against-'whichtthe-upper lip and lower lipfrespectively of the user maybe pressed while the telephone set is being used.

Another feature of. the noise shield consists in a variation'in thickness of its sidewalls. The wall portion adjacent-totheupper rolled edge 21 is relatively thiclnwhile thewallsection adjacent to the lowerrollededge 28 is relatively thin. The purpcseof the relativelyhthinwall section at the latter I point noted is-to impart increased compliance .andflexibility at.-thispoint inorder to allow the noise shield to move with the lower lip and chino! the: operator during-speech. .This eliminatesany tendency of thenoise shield to interfere with: properespeaking. while. at the same time excluding; ambientynoise and more efficiently transmittinglthe speech signal.

.An' annularchamber; 3&- isformed integrally with, and concentrically within',ithe:wal1 parts of thesyoice' chamber, forming a. rearward ,boundary of the voice chamber, theinner wall of. this chamber 3G-forminga rearward terminal part 5' of the 'voice chamber aligned with and leading :to the microphone. The-rearwall oirthe chamber! is planiform and'lies flat against aplaniform forward face'of the cap 1, At the forward side=of thefchamber 36; open tubular extensions 32 are formed, connectedto the side wall of the voice chamber, extending'forwardly; and opening intermediately of the front-to-reardimensionof the voice chamber. Two "of these extensions are shown'lo'cated adjacent a-horizontal diameter of the voice chamber so as to lie adjacent respective ends of the mouth of the user. Respective ducts 30 are formed through these extensions opening into the chamber 36, and in the rear wall of the chamber 36 there are formed four ports 34' somewhat larger in diameter than the ducts 30 two of which are opposite the ducts 30. Four equally spaced ducts 34 of smaller diameter than the ducts 30 are formed through the cap 1 opening from the ports 34', and two of which are nearly in line with the ducts 30 but slightly eccentric to the latter and two non-registering ducts 34 spaced midway between ducts 30.

The two sets of air ducts 30-34 constitute acoustical impedance elements analogous to electrical inductanccs, and the larger annular chamber 36 intermediate the two tubes constitutes an acoustical impedance element analogous to electrical capacitatnce, coactive with ducts 30-34. The combined effect of the two types of elements provides an acoustical low-pass filter whose function is to exclude high frequencies while permitting the operator to breathe freely. This filter arrangement greatly increases the efiiciency of the device in a high ambient noise field.

As a result of the relations and proportions of the ducts and the chamber 36, it may be seen that sound waves entering through the ducts 34 will expand considerably in the chamber 35, so that only a limited part will pass directly to the opposite ducts 30, and in addition interfering and outof-phase reflections and reaction waves will be returned to the passages 30 from the chamber 36. In addition, sound waves from the same external source those passing directly to the ducts 30, will be transmitted partly around the chamber 36 from the two non-registering ducts 34, which will reach the ducts 30 also out-of-phase with the directly transmitted waves, producing a pronounced interference and other levelling or neutralizing effects.

It should be also appreciated that the device will in some uses have importance in preventing unauthorized persons nearby from obtaining information by listening to the voice of the person using the microphone for the transmission of information. In such use the sound emanating from the voice chamber will be attenuated in the ducts 30, and leaving these will be diverted and diffused in the chamber 36, a small portion tending to escape through the directly opposite duct 34 and a part being reflected nearly reversely to the direction oi incidence, owing to the planiform surface surrounding the smaller duct 34 within the large ports 34'. This reversed sound will neutralize a substantial part of the sound leaving or in the ducts 30, and the reactive and diverslonal effects manifest in the chamber 36 will produce out-of-phase elements further contributing to neutralization. Eddies of air in the breath currents leaving the ducts 30 and engaging the surfaces around the ducts 34 in ports 34' will also contribute to dampening of sound from within the voice chamber passing through the ducts 30. In addition, the ducts 34 being smaller than the ducts 30, much of the escaping air and sound is forced to diverge from the axis of the ducts 30 and pass partly around the chamber 36 meeting currents and waves from the opposite direction and producing great damping action upon sound reaching this chamber, so that a very small amount of the air, and little if any sound, escape at the non-registering ducts 34.

It is intended that the noise shield member may be modified in various ways and utilized with other transmitting devices. The features described, such as the design of a correct acoustical cavity size to provide a proper response curve, may be used independently of the other features. Similarly, the acoustical low-pass filter may be applied to other devices where such a feature becomes desirable. In general, the size and s ape of the shield as well as the openings forming the low-pass filter are likewise subject to modification.

It will be seen that the features described provide an easily installed means of excluding ambient noise and thus improve transmission in a hand telephone set. Other advantages are also present which render the device more comfortable when held against the face and allow the shield to be maintained in. place for relatively long periods.

While I have shown a preferred embodiment of my invention, it should be understood that various changes and modifications may be resorted to, in keeping with the spirit of the invention as outlined in the appended claims.

Having thus described my invention, what I claim is:

1. A noise shield for a microphone or the like, comprising a compliant cup-shaped member adapted to be secured around the outer periphery of a microphone, said member having upper and lower rolled edges for engagement against the lips of an operator, the wall portions of said cupshaped member adjacent to said lower rolled edge being relatively thinner than the thickness of the wall portions adjacent to the upper rolled edge for the purpose of providing flexibility and whereby the lower side of said member may move with the lips and chin of the operator during use.

2. In a noise shield of the class described, a cup-shaped member adapted to be secured around the periphery of a microphone and shaped to engage the face of a wearer around his mouth to form a voice chamber, an annular chamber formed around the cup adjacent its outer wall and at the rearward part thereof, and around a space symmetrically extending forwardly from the microphone when engaged in the shield, said annular chamber constituting a rearward boundary of the voice chamber, ducts being formed on the inner wall of the voice chamber at diametrically opposite sides in communication with the voice chamber and the interior of the annular chamber, said annular chamber having a substantial dimension longitudinally of the noise shield, ports formed in the rear wall of said annular chamber, and a plurality of ducts of smaller diameter than the first named ducts but in greater number extending from the annular chamber rearwardly to the atmosphere.

PAUL S. VENEKLASEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,368,261 Jenkins Feb. 15, 1921 1,440,752 Stone Jan. 2, 1923 1,743,290 Stehllk Jan. 14, 1930 1,757,463 McCann 1 May 6, 1930 1,930,906 Nordenswan Oct. 17, 1933 2,390,488 Alfrod et a1 Dec. 11, 1945 2,398,076 Bulbulian Apr. 9, 1946 2,408,474 Newman et al Oct. 1, 1946 

